The rates of oxidation of 1:1 mixtures of associating thiols, each having the binding site (Remark: Graphics omitted.) and the recognition site [p-(CH3)2NC6H4 or R], with O2 were measured in 80% (v/v) acetonitrile-20% water in the range of 20 to 50 °C. Oxidation of the thiol having the p-(CH3)2NC6H4 group proceeds about 100 times faster than that of the thiols with R. It has been found that oxidation of 1:1 mixtures of the thiols is first-order with respect to thiols and 0.7 th-order with respect to triethylamine by means of the method of initial rates. The k1.7 values for R=C6H5, p-CH3C6H4, and p-C2H5C6H4 were similar to one another; this makes a sharp contrast with our previous work that the selectivity (the logarithmeric ratio of the yield of the unsymmetrical disulfide to twice that of the symmetrical disulfide) changes greatly with the structures of R and temperature. It is concluded that the product ratio does not depend upon the k1.7. The large negative activation entropies (−51 to −45 cal K−1 mol−1) suggest that the oxidation would proceed through a highly ordered transition state.
在 80%(v/v)
乙腈-20% 的
水中,在 20 至 50 °C的范围内,测量了各自具有结合位点(备注:图形省略)和识别位点[p-(
CH3)2NC6H4 或 R]的 1:1 结合
硫醇混合物与 O2 的氧化速率。通过初始速率法发现,1:1
硫醇混合物的氧化过程对
硫醇而言是一阶的,对
三乙胺而言是 0.7 阶的。R=
C6H5、对- C6H4 和对-C2H5C6H4 的 k1.7 值彼此相似;这与我们以前的工作形成了鲜明对比,即选择性(非对称二
硫化物的产率与对称二
硫化物的两倍产率的对数比)随 R 的结构和温度的变化而变化很大。由此得出结论,产物比与 k1.7 无关。较大的负活化熵(-51 至 -45 卡 K-1 mol-1)表明,氧化将通过高度有序的过渡态进行。